1. Field of the Invention
The present invention relates to the crosslinking of polymers using initiators, such as organic peroxides, and more specifically to the prevention of scorching in polymeric compositions, such as in compositions containing at least one polymer and at least one initiator. The present invention also relates to the use of allyl compounds as scorch retarders.
Still further, the present invention is directed to the formation of compositions which can be cross-linked, such as by heating, with reduced scorch, and to the resulting cross-linked polymers. Additionally, the present invention relates to the uses of the cross-linked polymers, such as for electrical insulation, industrial rubber products, e.g., hoses, belts, seals, and rotomolding plastic products.
2. Background Information
The production of crosslinked polymers is known in the art wherein the compositions forming the crosslinked polymers include, amongst other components, a polymeric component, and an initiator component. The problems with such compositions is that the compositions can undergo premature crosslinking, such as during compounding or processing, prior to the time in the processing when crosslinking of the composition is actually desired. For example, as discussed in U.S. Pat. Nos. 3,954,907 and 4,018,852, in order to process organic peroxide containing compositions so as to adapt them to be placed, as insulation, on the electrical conductor components of the wire and cable it is usually necessary to admix the components of the compositions at high temperatures, onto the electrical conductor. These processing activities occur prior to the intended vulcanization of the peroxide containing compositions, which is usually accomplished after such compositions are extruded onto the electrical conductor.
Scorch prevention can be accomplished by the use of additives in the composition acting as scorch retarders to prevent or reduce the premature crosslinking of the polymeric compositions. For example, U.S. Pat. No. 3,954,907 to Schober discloses that vulcanizable ethylene polymer based compositions which employ certain classes of organic peroxides therein as vulcanizing agents, and which compositions are susceptible to scorching under a given set of conditions, can be protected against scorching under such conditions by incorporating in such compositions certain monomeric monofunctional vinyl compounds.
Monomeric monofunctional vinyl compounds scorch retarders according to U.S. Pat. No. 3,954,907 include unsaturated additives such as lauryl methacrylate, .alpha.-methyl styrene, and n-butyl methacrylate, whereas compounds such as allyl caprylate and allyl phenyl ether are disclosed to produced little or no increase, if not a decrease, in an efficiency value disclosed therein.
U.S. Pat. No. 4,018,852 to Shober discloses that vulcanizable ethylene polymer based compositions which employ certain classes of organic peroxides therein as vulcanizing agents, and which compositions are susceptible to scorching under a given set of conditions, can be protected against scorching under such conditions by incorporating in such compositions certain classes of organic hydroperoxides and organic compounds containing at least three allyl groups.
Still further, other documents, such as U.S. Pat. No. 5,516,845 to Heese disclose coagents, such as triallylcyanurates, which do not function as scorch retarders, in polymeric compositions that are to be crosslinked.
While it is known to include various scorch retarders and coagents in crosslinkable polymeric compositions, there is still a need in the art to provide scorch retarders and compositions containing scorch retarders wherein the crosslinked polymer can maintain a high cross-link density.